1. Field of the Invention
This invention relates generally to transfer drive mechanisms and, more specifically, to cam-actuated pick-and-place drive mechanisms for imparting linear motion along two mutually perpendicular axes.
2. Description of the Prior Art
Linear pick-and-place devices have long been used to achieve automated transfer of articles, such as assembly components or tools in fully or partly automated manufacturing processes. They provide precision to a tedious task of repetitively moving a series of objects from one location to another nearby location. While various attempts have been made to improve the output, weight capacity, and performance of these linear pick-and-place devices, little has been done to optimize their manufacturing costs, serviceability and reliability. One drawback of existing linear pick-and-place devices is that the overall dimensions of the devices, including the housing (or so-called "envelope") tend to be relatively large, making a big "footprint," i.e. a relatively large amount of floor space at an assembly plant is occupied by the device. In part, the large dimensions of linear pick-and-place devices can be attributed to the fact that the devices include two cams, one for directing motion in a first, or x-direction, and another for directing motion in a second, or y-direction.
A useful improvement in the history of the development of linear pick-and-place devices has been the advent of adjustable stroke lengths for such devices. By being able to set the stroke lengths either at the site of manufacture prior to shipment, or better yet, by the end user, such linear pick-and-place devices have been able to meet demand to perform tasks in a variety of specific assembly settings without the need for individual customized manufacture. Generally, adjustability has been achieved using an infinitely adjustable slide block mounted on the edge of a first carriage. The infinitely adjustable slide block may incorporate a movable pivot slide, such as a threadedly-mounted pivot slide that is used in conjunction with a threaded rod, as typified in U.S. Pat. Nos. 3,751,996 and 3,881,362, to control the range of translational movement, or lift movement, or both.
A drawback of these infinitely adjustable slide blocks is that the increased mass of the threaded rod and pivot slide result in increased inertia in the corresponding arm that controls either translational or lift movement. This relatively high inertia in the arm member, in turn, tends to require a higher capacity motor and reducer to operate the drive shaft that controls movement of the corresponding cam. Another drawback is that the slide block needs to be locked in place along the threaded rod. Fastening means, such as an allen bolt or cotter pin, is required. Should the fastening means become loose, the slide block may slip, particularly if the threads of the threaded rod become stripped over time, in which case positioning accuracy is lost. This would likely have a detrimental effect on quality control of the overall assembly process in which the linear pick-and-place drive is used.
The manner in which these and other drawbacks of prior adjustable linear pick-and-place devices are overcome by the present invention is set forth in the following Summary of the Invention, the Drawings, and the Detailed Description of the Preferred Embodiment.